In the next-generation wireless communication systems in which high-speed transmission at the transmission rates of 100 Mbits/sec to 1 Gbits/sec is required, allocation of high-frequency bands is assumed. However, it is known that the signals in high-frequency bands generally exhibit strong straightness compared with the signals in low-frequency bands, so that many blind zones (to which radio waves do not reach) can occur. Therefore, the allocation of high-frequency bands reduces the cellular coverage (service area) in the case where the transmission power at the base station is identical to the transmission power in the wireless transmission systems currently in commercial use. The reduction in the cellular coverage is undesirable because the reduction in the cellular coverage leads to frequent occurrence of handovers as well as cost increase due to increase in the number of base stations.
In consideration of the above problem, a wireless communication system having a wireless relay device which relays wireless communication between a base station and mobile station has been proposed. Since the cost of the wireless relay device is generally lower than the cost of the base station, introduction of the wireless relay device enables securing of a sufficient coverage and realization of the entire system at low cost. The wireless communication system having a wireless relay device is currently studied in the IEEE 802.16j task group. The information under study is disclosed on IEEE 802.16 standard documents.
The diversity is known as a technique for securing quality of wireless communication in fading channel. In particular, the transmission diversity using two or more transmission antennas is currently used in the mobile communication systems since the receiving stations are not required to increase the number of antennas. However, conventionally the use of the transmission diversity in the wireless relay device has not been considered. If two transmission antennas are arranged in a wireless relay device for transmitting an identical signal to a receiving station through the two transmission antennas, signals which have passed through multiple paths are received by the receiving station, so that desired reception performance (reduction of the code error rate) which is expected with the transmission diversity cannot be achieved.